The antonym for the word "unlooses" is "fastens." Loosening implies the release of tension or restraint, while fastening indicates the securing of an object or tightening its grip. For instance, if you unloose a knot, you are freeing it from its entanglement, whereas if you fasten the knot, you are locking it in place. Similarly, if you unloose a bolt, you are removing it from its position, whereas if you fasten the bolt, you are tightening it. In other words, the opposite of unlooses is to bind, attach, or clinch, depending on the context.